This program is designed to investigate the major causes and mechanisms of pulmonary cancer in man through the study of lung cancer induced in animals. A variety of inhaled air-pollutants that are petroleum-soluble and other carcinogens are being studied by incorporation into melted beeswax which can be infiltrated into the lung or other organs to be retained with slow release over long periods of time. Secondly, we continue to investigate those properties of fibers critical to pulmonary and pleural carcinogenesis. Factors of special concern this year have been the role that macrophages play in particulate invasion of the lung. Examination of commercial products for the presence of fibers in the critical range has been started.